Introduction

The catch-all term “intervertebral disc disease” (IVDD) is familiar to all veterinary clinicians, but lacks any specificity of definition. It does not convey whether the “disease” is clinical or subclinical, and it neither addresses the seriousness of the problem nor offers any useful prognostic information or suggestions for proper intervention. Within the rubric of “IVDD” are other terms such as “prolapse,” “rupture,” “herniation,” and “bulge” that are often used synonymously or with great overlap.

Devising and using appropriate nomenclature for abnormalities associated with the intervertebral disc has been an uncommonly addressed topic in veterinary medicine. In human medicine, this subject was largely avoided until efforts were made in the late 1990s by the American Society of Spine Radiology (ASSR) to develop a standardized glossary of terms that could be applied to imaging studies of the human lumbar intervertebral disc [1–3]. There were several reasons that basic scientists and physicians attempted to improve the nomenclature used to describe intervertebral disc pathology [4]. First, by standardizing reporting terms, heterogeneity in disease description is reduced. This has an immediate, positive effect on the quality of clinical and research data. Second, compelling clinicians to use the same terms for similar diseases facilitates communication with colleagues, paraprofessionals, and clients. Finally, by improving data quality and communication, standardized terminology is likely to enhance care delivery.

Several guiding principles should be used to develop appropriate nomenclature [5]. Importantly, terminology should be based on previously approved anatomical descriptors, such as those in the Nomina Anatomica Veterinaria. If at all possible, terms should have a basis in pathomechanisms and should not be eponymous. Medical vocabulary should allow clinicians to distinguish similar diseases that may have divergent outcomes or treatments. Finally, in veterinary medicine, adhering to systems commonly used by physicians and basic scientists is likely to be advantageous. Shared nomenclature, similar to what has been attempted by the World Health Organization (WHO) Classification of Tumors of Domestic Animals, facilitates comparative medical studies and communication with those in other medical professions.

The goals of this chapter are to review the history of nomenclature associated with intervertebral disc pathology in dogs and to discuss current, appropriate terms based upon available veterinary and human medical literature.

A brief history of nomenclature for intervertebral disc displacement in dogs

To the authors’ knowledge, the first report of canine intervertebral disc displacement occurred in 1881, when Janson described a young dachshund that was euthanized due to acute onset paraplegia [6]. Janson thought that the lesion grossly compressing the spinal cord resembled a cartilaginous tumor and termed it an enchondroma of the intervertebral disc. In 1893, Dexler described “pachymeningitis chronica ossificans” that resulted in spinal cord compression and was associated with mineralized material originating from the intervertebral disc [6]. In the early twentieth century, several investigators reported the presence of similar cartilaginous or mineralized debris in the epidural space of dogs with paraplegia. The presence of this material was referred to as “enostosis intervertebralis,” “ekchondrosis intervertebralis,” “calcinosis intervertebralis,” and “ekchondroma.” Small studies by Olsson [7] and McGrath [8] in the early 1950s used terms such as “disc protrusion” or “intervertebral disc syndrome” to describe spinal cord compression secondary to disc displacement in dogs.

Even 60 years after Hansen’s seminal work on intervertebral disc degeneration and introduction of the term “herniation” (intervertebral disc herniation (IVDH)) in dogs, his influence remains well entrenched [6]. Hansen described the histology and structure of the nucleus pulposus, annulus fibrosus, and cartilaginous end plate. He attempted to define disc degeneration, although he noted, “it is practically impossible to give a certain and detached definition.” Hansen subclassified degeneration as fibroid or chondroid and associated these phenotypes with signalment features. Additionally, two types of IVDH were defined, Hansen type I and Hansen type II. As described, type I and type II IVDH are essentially synonymous with the modern terms “extrusive” and “protrusive” IVDH, respectively.

Much of the nomenclature proposed by Hansen does not meet modern, generally agreed upon criteria for appropriate medical terminology. For example, the descriptors “IVDH,” “disc prolapse,” and “disc protrusion” were used interchangeably by Hansen. Today, the ASSR defines disc herniation and disc protrusion as related, but distinct entities and does not recognize the term disc prolapse. Importantly, while many veterinary clinicians and students still describe canine IVDH as either type I or type II, this nomenclature is not accepted by ASSR, is not in common use outside veterinary medicine, and does not necessarily reflect underlying pathomechanisms [1].